Liquid solder resist composition and covered-printed wiring board

ABSTRACT

A liquid solder resist composition contains a carboxyl group-containing resin, a photopolymerizable compound containing at least one compound selected from a group consisting of a photopolymerizable monomer and a photopolymerizable prepolymer, a photopolymerization initiator, a titanium dioxide, and a compound having a cyclic ether skeleton. The titanium dioxide contains both of a rutile titanium dioxide manufactured by a sulfuric acid method and a rutile titanium dioxide manufactured by a chlorine method.

TECHNICAL FIELD

The present invention relates to a liquid solder resist composition anda covered-printed wiring board, and specifically relates to a liquidsolder resist composition that has photocurability and can be developedusing an alkaline solution, and a covered-printed wiring board thatincludes a solder resist layer made of the liquid solder resistcomposition.

BACKGROUND ART

In recent years, as a method for forming solder resist layers onprinted-wiring boards for consumer use and industrial use, a methodusing a liquid solder resist composition that has excellent resolution,size precision, and the like, and can be developed has been widelyadopted, instead of a screen printing method, in order to increase thedensity of wiring on the printed-wiring board.

Also, in recent years, optical elements such as light-emitting diodesare often mounted directly on a printed-wiring board on which a solderresist layer is formed to cover the printed-wiring board, for uses in:backlights of liquid crystal displays of mobile terminals, personalcomputers, televisions, and the like; light sources of illuminationdevices; and the like. Furthermore, as a result of the solder resistlayer of the printed-wiring board on which optical elements are mountedcontaining titanium dioxide, the solder resist layer is whitened, whichallows light emitted from light-emitting elements to efficiently reflectoff the solder resist layer (see JP2011-17010A, JP4657358B,JP2011-215384A).

SUMMARY OF INVENTION

There exist two kinds of titanium dioxides depending on manufacturingmethods such as a sulfuric acid method (liquid phase method) and achlorine method (gas phase method). There also exist other two kinds oftitanium dioxides, which are a rutile titanium dioxide and an anatasetitanium dioxide, depending on crystal structure.

However, there is a problem that a solder resist layer containing therutile titanium dioxide manufactured by the sulfuric acid method has lowlight reflectivity even though it has less deterioration due toultraviolet rays and heat.

Also, there are problems that, even though a solder resist layercontaining the rutile titanium dioxide manufactured by the chlorinemethod has high reflectivity, the light reflectivity decreased due toultraviolet rays irradiation and thus it is difficult to maintain thehigh reflectivity and the solder resist layer easily turns its color toyellow due to ultraviolet rays.

Furthermore, there is a problem that a solder resist layer containingthe anatase titanium dioxide is originally not white but yellowish, haslarge deterioration of a coating film due to ultraviolet rays and heat,and has low light reflectivity.

The present invention has been made in light of the above-describedcircumstances, and it is an object thereof to provide a liquid solderresist composition capable of forming a solder resist layer that hashigh reflectivity with suppressed deterioration especially due to light,and to provide a covered-printed wiring board including a solder resistlayer made of the liquid solder resist composition.

The liquid solder resist composition according to the present inventionincludes a carboxyl group-containing resin, a photopolymerizablecompound containing at least one compound selected from a groupconsisting of a photopolymerizable monomer and a photopolymerizableprepolymer, a photopolymerization initiator, a titanium dioxide, and acompound having a cyclic ether skeleton, and the titanium dioxidecontains both of a rutile titanium dioxide manufactured by a sulfuricacid method and a rutile titanium dioxide manufactured by a chlorinemethod.

The covered-printed wiring board according to the present inventionincludes a printed-wiring board and a solder resist layer that coversthe printed-wiring board, and the solder resist layer is made of theabove-described liquid solder resist composition.

DESCRIPTION OF EMBODIMENTS

An embodiment for implementing the present invention will now bedescribed.

A liquid solder resist composition according to this embodiment containsa carboxyl group-containing resin, a photopolymerizable compound, aphotopolymerization initiator, a titanium dioxide, and a compound havinga cyclic ether skeleton. Each of the components is described further indetain hereinafter. It should be noted that in the present invention,“(meth)acryl” means at least one selected from “acryl” and “methacryl”and “(meth)acrylate” means at least one selected from “acrylate” and“methacrylate”.

The carboxyl group-containing resin can provide the coating film made ofthe liquid solder resist composition with a capability of beingdeveloped using an alkaline solution, or in other words, with analkaline development capability.

The carboxyl group-containing resin can contain a compound that has acarboxyl group and that is not photopolymerizable (hereinafter, referredto as (A1) component).

The (A1) component contains, for example, polymer of an ethylene-basedunsaturated monomer that contains an ethylene-based unsaturated compoundhaving a carboxyl group. Furthermore, the ethylene-based unsaturatedmonomer may contain an ethylene-based unsaturated compound that does nothave a carboxyl group.

The ethylene-based unsaturated compound having a carboxyl group cancontain an appropriate polymer and prepolymer, and for example, cancontain a compound that has only one ethylene-based unsaturated group.More specifically, for example, the ethylene-based unsaturated compoundhaving a carboxyl group can contain at least one compound selected fromthe group consisting of acrylic acid, methacrylic acid,ω-carboxy-polycaprolactone (n≈2) monoacrylate, crotonic acid, cinnamicacid, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate,2-acryloyloxyethyl phthalate, 2-methacryloyloxyethyl phthalate,2-acryloyloxypropyl phthalate, 2-methacryloyloxypropyl phthalate,2-acryloyloxyethyl maleate, 2-methacryloyloxyethyl maleate,β-carboxyethyl acrylate, 2-acryloyloxyethyl tetrahydrophthalate,2-methacryloyloxyethyl tetrahydrophthalate, 2-acryloyloxyethylhexahydrophthalate, and 2-methacryloyloxyethyl hexahydrophthalate. Theethylene-based unsaturated compound having a carboxyl group can alsocontain a compound having a plurality of ethylene-based unsaturatedgroups. More specifically, for example, the ethylene-based unsaturatedcompound having a carboxyl group can contain a compound obtained bycausing polyfunctional (meth)acrylate having a hydroxyl group selectedfrom the group consisting of pentaerythritol triacrylate,pentaerythritol trimethacrylate, trimethylolpropane diacrylate,trimethylolpropane dimethacrylate, dipentaerythritol pentaacrylate, anddipentaerythritol pentamethacrylate to react with a dibasic acidanhydride. These compounds are used alone or in combination.

It is sufficient that the ethylene-based unsaturated compound that doesnot have a carboxyl group is a compound that is able to be copolymerizedwith an ethylene-based unsaturated compound having a carboxyl group. Theethylene-based unsaturated compound that does not have a carboxyl groupcan contain a compound that has an aromatic ring and/or a compound thatdoes not have an aromatic ring.

The compound that has an aromatic ring can contain at least one compoundselected from the group consisting of2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, benzyl(meth)acrylate, neopentyl glycol benzoate (meth)acrylate,paracumylphenoxyethylene glycol (meth)acrylate, EO-modified cresol(meth)acrylate, ethoxylated phenyl (meth)acrylate, nonylphenoxypolyethylene glycol (meth)acrylate (n=2 to 17), ECH-modified phenoxy(meth)acrylate, phenoxy diethylene glycol (meth)acrylate, phenoxyethyl(meth)acrylate, phenoxy hexaethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, tribromophenyl (meth)acrylate,EO-modified tribromophenyl (meth)acrylate, EO-modified bisphenol Adi(meth)acrylate, PO-modified bisphenol A di(meth)acrylate, modifiedbisphenol A di(meth)acrylate, EO-modified bisphenol F di(meth)acrylate,ECH-modified phthalic acid di(meth)acrylate, trimethylolpropane benzoate(meth)acrylate, EO-modified phthalic acid (meth)acrylate, EO/PO-modifiedphthalic acid (meth)acrylate, N-phenylmaleimide, N-benzylmaleimide,N-vinylcarbazole, styrene, vinylnaphthalene, and 4-vinylbiphenyl, forexample.

The compound that does not have an aromatic ring can contain at leastone compound selected from the group consisting of linear or branchedaliphatic or alicyclic (which may include a ring having an unsaturatedbond) (meth)acrylic acid esters, hydroxyalkyl (meth)acrylates, andalkoxyalkyl (meth)acrylates, and N-substituted maleimides such asN-cyclohexylmaleimide, for example. The compound that does not have anaromatic ring may contain a compound having two or more ethylene-basedunsaturated groups in one molecule, such as polyethylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, and pentaerythritoltri(meth)acrylate. These compounds are used alone or in combination.These compounds are preferable in that the hardness and oiliness of thesolder resist layer are easily adjusted.

Types, ratios, and the like of a compound used to obtain the (A1)component are appropriately selected such that the acid value of the(A1) component has an appropriate value. The acid value of the (A1)component is preferably within a range of 20 to 180 mgKOH/g, and morepreferably within a range of 35 to 165 mgKOH/g.

The carboxyl group-containing resin can also contain aphotopolymerizable carboxyl group-containing resin (hereinafter,referred to as a (A2) component) having a carboxyl group and aphotopolymerizable functional group. The photopolymerizable functionalgroup is an ethylene-based unsaturated group, for example.

The (A2) component can contain, for example, a resin (hereinafter,referred to as a first resin (a)) having a structure obtained by: atleast one of epoxy groups in an epoxy compound (a1) having two or moreepoxy groups in one molecule being reacted with an ethylene-basedunsaturated compound (a2) having a carboxyl group; and at least onecompound (a3) selected from a group consisting of polyvalent carboxylicacids and anhydrides thereof being further added to the reactionproduct.

The epoxy compound (a1) can contain at least one compound selected fromthe group consisting of cresol novolac epoxy resins, phenol novolacepoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins,bisphenol A-novolac epoxy resins, naphthalene epoxy resins, biphenylepoxy resins, biphenyl aralkyl epoxy resins, triglycidyl isocyanurate,alicyclic epoxy resins, and a polymer of an ethylene-based unsaturatedcompound containing a compound having an epoxy group, for example.

The epoxy compound (a1) may contain the polymer of the ethylene-basedunsaturated compound (p) containing the compound (p1) having an epoxygroup. The ethylene-based unsaturated compound (p) that is provided inthe synthesis of this polymer may only contain the compound (p1) havingan epoxy group, or may contain the compound (p1) having an epoxy groupand a compound (p2) that does not have an epoxy group.

The compound (p1) having an epoxy group can contain a compound selectedfrom appropriate polymers and prepolymers. Specifically, the compound(p1) having an epoxy group can contain at least one compound selectedfrom the group consisting of epoxycyclohexyl derivatives of acrylicacid, epoxycyclohexyl derivatives of methacrylic acid, alicyclic epoxyderivatives of acrylate, alicyclic epoxy derivatives of methacrylate,β-methylglycidyl acrylate, and β-methylglycidyl methacrylate. Inparticular, it is preferable that the compound (p1) having an epoxygroup contains glycidyl (meth)acrylate that is generally used and can beeasily obtained.

It is sufficient that the compound (p2) that does not have an epoxygroup is a compound that can copolymerize with the compound (p1) havingan epoxy group. The compound (p2) that does not have an epoxy group cancontain at least one compound selected from the group consisting of2-(meth)acryloyloxyethyl phthalate,2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate,2-(meth)acryloyloxypropyl phthalate, benzyl (meth)acrylate, neopentylglycol benzoate (meth)acrylate, paracumylphenoxyethylene glycol(meth)acrylate, EO-modified cresol (meth)acrylate, ethoxylated phenyl(meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate (degreeof polymerization n=2 to 17), ECH-modified phenoxy (meth)acrylate,phenoxy diethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate,phenoxy hexaethylene glycol (meth)acrylate, phenoxy tetraethylene glycol(meth)acrylate, tribromophenyl (meth)acrylate, EO-modifiedtribromophenyl (meth)acrylate, EO-modified bisphenol A di(meth)acrylate,PO-modified bisphenol A di(meth)acrylate, modified bisphenol Adi(meth)acrylate, EO-modified bisphenol F di(meth)acrylate, ECH-modifiedphthalic acid di(meth)acrylate, trimethylolpropane benzoate(meth)acrylate, EO-modified phthalic acid (meth)acrylate, EO/PO-modifiedphthalic acid (meth)acrylate, vinylcarbazole, styrene,N-phenylmaleimide, N-benzylmaleimide, 3-maleimide benzoic acidN-succinimidyl, linear or branched aliphatic or alicyclic (which mayinclude a ring having an unsaturated bond) (meth)acrylic acid esters,hydroxyalkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, andN-substituted maleimides (for example, N-cyclohexylmaleimide), forexample.

The compound (p2) that does not have an epoxy group may contain acompound having two or more ethylene-based unsaturated groups in onemolecule. As a result of this compound being used and the amount thereofbeing adjusted, the hardness and oiliness of the solder resist layer iseasily adjusted. The compound having two or more ethylene-basedunsaturated groups in one molecule can contain at least one compoundselected from the group consisting of polyethylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, and pentaerythritoltri(meth)acrylate, for example.

Polymers can be obtained by the ethylene-based unsaturated compound (p)being polymerized by a known polymerization method such as a solutionpolymerization method or an emulsion polymerization method, for example.Specific examples of solution polymerization methods include a method inwhich the ethylene-based unsaturated compound (p) is heated and stirredin an appropriate organic solvent with a polymerization initiator undera nitrogen atmosphere, and an azeotropic polymerization method.

An organic solvent used for polymerization of the ethylene-basedunsaturated compound (p) can contain at least one compound selected fromthe group consisting of ketones such as methylethyl ketone andcyclohexanone, aromatic hydrocarbons such as toluene and xylene, acetateesters such as ethyl acetate, butyl acetate, cellosolve acetate, butylcellosolve acetate, carbitol acetate, butyl carbitol acetate, andpropylene glycol monomethyl ether acetate, and dialkylglycol ethers, forexample.

The polymerization initiator used for polymerization of theethylene-based unsaturated compound (p) can contain at least onecompound selected from the group consisting of hydroperoxides such asdiisopropyl benzene hydroperoxide, dialkyl peroxides such as dicumylperoxide and 2,5-dimethyl-2,5-di-(t-butylperoxy)-hexane, diacylperoxides such as isobutyryl peroxide, ketone peroxides such as methylethyl ketone peroxide, alkyl peresters such as t-butyl peroxypivalate,peroxydicarbonates such as diisopropyl peroxydicarbonate, azo compoundssuch as azobisisobutyronitrile, and redox-system initiators, forexample.

The ethylene-based unsaturated compound (a2) can contain a compoundselected from the group consisting of appropriate polymers andprepolymers. The ethylene-based unsaturated compound (a2) can contain acompound having only one ethylene-based unsaturated group. The compoundhaving only one ethylene-based unsaturated group can contain at leastone compound selected from the group consisting of acrylic acid,methacrylic acid, crotonic acid, cinnamic acid, 2-acryloyloxyethylsuccinate, 2-methacryloyloxyethyl succinate, 2-acryloyloxyethylphthalate, 2-methacryloyloxyethyl phthalate, β-carboxyethyl acrylate,2-acryloyloxyethyl tetrahydrophthalate, 2-methacryloyloxyethyltetrahydrophthalate, 2-acryloyloxyethyl hexahydrophthalate, and2-methacryloyloxyethyl hexahydrophthalate, for example. Theethylene-based unsaturated compound (a2) can contain a compound having aplurality of ethylene-based unsaturated groups. The compound having theplurality of ethylene-based unsaturated groups can contain at least onecompound selected from the group consisting of compounds obtained bycausing polyfunctional acrylates and polyfunctional methacrylates thathave a hydroxyl group, such as pentaerythritol triacrylate,pentaerythritol trimethacrylate, trimethylolpropane diacrylate,trimethylolpropane dimethacrylate, dipentaerythritol pentaacrylate, anddipentaerythritol pentamethacrylate to react with a dibasic acidanhydride, for example.

In particular, it is preferable that the ethylene-based unsaturatedcompound (a2) contains at least one of acrylic acid and methacrylicacid. In this case, the ethylene-based unsaturated group derived fromacrylic acid and methacrylic acid has excellent photoreactivity inparticular, and thus the first resin (a) has high photoreactivity.

The usage amount of the ethylene-based unsaturated compound (a2) ispreferably within a range of 0.4 to 1.2 mol of the carboxyl group in theethylene-based unsaturated compound (a2) relative to 1 mol of the epoxygroup in the epoxy compound (a1), and preferably particularly within arange of 0.5 to 1.1 mol of the carboxyl group relative to 1 mol of theepoxy group.

The compound (a3) selected from the group consisting of polyvalentcarboxylic acids and anhydrides thereof can contain at least onecompound selected from the group consisting of dicarboxylic acids suchas phthalic acid, tetrahydrophthalic acid, methyltetrahydrophthalicacid, methylnadic acid, hexahydrophthalic acid, methyl hexahydrophthalicacid, succinic acid, methylsuccinic acid, maleic acid, citraconic acid,glutaric acid, and itaconic acid; polyvalent carboxylic acids oftribasic acids or greater polyvalent carboxylic acids such ascyclohexane-1,2,4-tricarboxylic acid, trimellitic acid, pyromelliticacid, benzophenone tetracarboxylic acid, and methylcyclohexenetetracarboxylic acid; and anhydrides of these polyvalent carboxylicacids.

The compound (a3) is used mainly for the purpose of giving an acid valueto the first resin (a) so that the liquid solder resist compositionre-disperses and re-dissolves in a dilute aqueous alkaline solution. Theusage amount of the compound (a3) is adjusted such that the first resin(a) preferably has an acid value of 30 mgKOH/g or greater, andparticularly preferably has an acid value of 60 mgKOH/g or greater.Also, the usage amount of the compound (a3) is adjusted such that thefirst resin (a) preferably has an acid value of 160 mgKOH/g or less, andparticularly preferably 130 mgKOH/g or less.

When the first resin (a) is synthesized, a known method can be adoptedto cause the addition reaction between the epoxy compound (a1) and theethylene-based unsaturated compound (a2) and the addition reactionbetween the product resulting from this addition reaction (additionreaction product) and the compound (a3) to progress. For example, at thetime of the addition reaction between the epoxy compound (a1) and theethylene-based unsaturated compound (a2), the ethylene-based unsaturatedcompound (a2) is added to the solvent solution of the epoxy compound(a1), and a thermal polymerization inhibitor and a catalyst are furtheradded as needed, and then the mixture is stirred and mixed to obtain areactive solution. As a result of causing the reaction of this reactivesolution using a usual method at a reaction temperature of preferably 60to 150° C., and particularly preferably 80 to 120° C., the additionreaction product can be obtained. Examples of the thermal polymerizationinhibitor include hydroquinone and hydroquinone monomethyl ether.Examples of the catalyst include tertiary amines such asbenzyldimethylamine and triethylamine, quaternary ammonium salts such astrimethylbenzylammonium chloride and methyltriethylammonium chloride,triphenylphosphine, and triphenyl stibine.

When the addition reaction between the addition reaction product and thecompound (a3) is caused to progress, the compound (a3) is added to thesolvent solution containing the addition reaction product, a thermalpolymerization inhibitor and a catalyst are further added as needed, andthen the mixture is stirred and mixed to obtain a reactive solution. Asa result of causing the reaction of the reactive solution using a usualmethod, the first resin (a) can be obtained. It is sufficient thatreaction conditions are the same as those for the case of the additionreaction between the epoxy compound (a1) and the ethylene-basedunsaturated compound (a2). The compounds used at the time of theaddition reaction between the epoxy compound (a1) and the ethylene-basedunsaturated compound (a2) having a carboxyl group can be used as is, asthe thermal polymerization inhibitor and the catalyst.

The (A2) component may contain a carboxyl group-containing(meth)acryl-based copolymer resin (referred to as a second resin (b))obtained by causing a portion of carboxyl groups in the polymer of anethylene-based unsaturated monomer containing an ethylene-basedunsaturated compound having a carboxyl group to react with anethylene-based unsaturated compound having an epoxy group. Theethylene-based unsaturated monomer may also include an ethylene-basedunsaturated compound that does not have a carboxyl group as needed.

The ethylene-based unsaturated compound having a carboxyl group forobtaining the second resin (b) can contain an appropriate polymer and/orprepolymer. For example, the ethylene-based unsaturated compound havinga carboxyl group can contain a compound having only one ethylene-basedunsaturated group. More specifically, the ethylene-based unsaturatedcompound having a carboxyl group can contain at least one compoundselected from the group consisting of acrylic acid, methacrylic acid,ω-carboxy-polycaprolactone (n≈2) monoacrylate, crotonic acid, cinnamicacid, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate,2-acryloyloxyethyl phthalate, 2-methacryloyloxyethyl phthalate,β-carboxyethyl acrylate, 2-acryloyloxypropyl phthalate,2-methacryloyloxypropyl phthalate, 2-acryloyloxyethyl maleate,2-methacryloyloxyethyl maleate, 2-acryloyloxyethyl tetrahydrophthalate,2-methacryloyloxyethyl tetrahydrophthalate, 2-acryloyloxyethylhexahydrophthalate, and 2-methacryloyloxyethyl hexahydrophthalate, forexample. The ethylene-based unsaturated compound having a carboxyl groupcan contain a compound having a plurality of ethylene-based unsaturatedgroups. More specifically, for example, the ethylene-based unsaturatedcompound having a carboxyl group can contain a compound obtained bycausing polyfunctional (meth)acrylate having a hydroxyl group selectedfrom the group consisting of pentaerythritol triacrylate,pentaerythritol trimethacrylate, trimethylolpropane diacrylate,trimethylolpropane dimethacrylate, dipentaerythritol pentaacrylate, anddipentaerythritol pentamethacrylate to react with a dibasic acidanhydride. These compounds are used alone or in combination.

It is sufficient that the ethylene-based unsaturated compound that doesnot have a carboxyl group for obtaining the second resin (b) is acompound that can copolymerize with the ethylene-based unsaturatedcompound having a carboxyl group. The ethylene-based unsaturatedcompound that does not have a carboxyl group can contain a compound thathas an aromatic ring and/or a compound that does not have an aromaticring.

The compound that has an aromatic ring can contain at least one compoundselected from the group consisting of2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, benzyl(meth)acrylate, neopentyl glycol benzoate (meth)acrylate,paracumylphenoxyethylene glycol (meth)acrylate, EO-modified cresol(meth)acrylate, ethoxylated phenyl (meth)acrylate, nonylphenoxypolyethylene glycol (meth)acrylate (n=2 to 17), ECH-modified phenoxy(meth)acrylate, phenoxy diethylene glycol (meth)acrylate, phenoxyethyl(meth)acrylate, phenoxy hexaethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, tribromophenyl (meth)acrylate,EO-modified tribromophenyl (meth)acrylate, EO-modified bisphenol Adi(meth)acrylate, PO-modified bisphenol A di(meth)acrylate, modifiedbisphenol A di(meth)acrylate, EO-modified bisphenol F di(meth)acrylate,ECH-modified phthalic acid di(meth)acrylate, trimethylolpropane benzoate(meth)acrylate, EO-modified phthalic acid (meth)acrylate, EO/PO-modifiedphthalic acid (meth)acrylate, N-phenylmaleimide, N-benzylmaleimide,N-vinylcarbazole, styrene, vinylnaphthalene, and 4-vinylbiphenyl, forexample.

The compound that does not have an aromatic ring can contain at leastone compound selected from the group consisting of linear or branchedaliphatic or alicyclic (which may include a ring having an unsaturatedbond) (meth)acrylic acid esters, hydroxyalkyl (meth)acrylates, andalkoxyalkyl (meth)acrylates, and N-substituted maleimides such asN-cyclohexylmaleimide, for example. The compound that does not have anaromatic ring may contain a compound having two or more ethylene-basedunsaturated groups in one molecule, such as polyethylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, and pentaerythritoltri(meth)acrylate. These compounds are used alone or in combination.These compounds are preferable in that the hardness and oiliness of thesolder resist layer are easily adjusted.

Examples of the ethylene-based unsaturated compound having an epoxygroup for obtaining the second resin (b) include appropriate polymersand prepolymers. Specific examples of the ethylene-based unsaturatedcompound having an epoxy group include epoxycyclohexyl derivatives ofacrylic acid or methacrylic acid; alicyclic epoxy derivatives ofacrylate or methacrylate; β-methylglycidyl acrylate, andβ-methylglycidyl methacrylate. These compounds are used alone or incombination. In particular, it is preferable to use glycidyl(meth)acrylate that is generally used and can be easily obtained.

The (A2) component may contain a resin (hereinafter, referred to as athird resin (c)) obtained by adding a compound having an ethylene-basedunsaturated group and an isocyanate group to a portion or all ofhydroxyl groups in a polymer of an ethylene-based unsaturated monomerthat contains both an ethylene-based unsaturated compound having acarboxyl group and an ethylene-based unsaturated compound having ahydroxyl group. The ethylene-based unsaturated monomer may contain anethylene-based unsaturated compound that does not have a carboxyl groupnor hydroxyl group as needed.

Examples of the ethylene-based unsaturated compound having a carboxylgroup for obtaining the third resin (c) may be the same as those recitedfor the ethylene-based unsaturated compound having a carboxyl group forobtaining the second resin (b) described above, for example.

Specific examples of the ethylene-based unsaturated compound having ahydroxyl group for obtaining the third resin (c) include hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, cyclohexanedimethanolmono(meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethylphtalate,caprolactone (meth)acrylate, polyethylene glycol (meth)acrylate,polypropylene glycol (meth)acrylate, trimethylolpropanedi(meth)acrylate, pentaerythritol tri(meth)acrylate, anddipentaerythritol penta(meth)acrylate; hydroxybutyl vinyl ether;hydroxyethyl vinyl ether, and N-hydroxyethyl (meth)acrylamide.

Specific examples of the compound having an ethylene-based unsaturatedgroup and an isocyanate group for obtaining the third resin (c) include2-acryloyloxyethyl isocyanate (specific examples include part number“Karenz AOI” (Showa Denko K.K.)), 2-methacryloyloxyethyl isocyanate(specific examples include part number “Karenz MOI” (Showa Denko K.K.)),methacryloyloxyethoxyethyl isocyanate (specific examples include partnumber “Karenz MOI-EG” (Showa Denko K.K.)), an isocyanate block body ofKarenz MOI (specific examples include part number “Karenz MOI-BM” (ShowaDenko K.K.)), an isocyanate block body of Karenz MOI (specific examplesinclude part number “Karenz MOI-BP” (Showa Denko K.K.), and1,1-(bisacryloyloxymethyl)ethyl isocyanate) (specific examples includepart number “Karenz BEI” (Showa Denko K.K.)).

It is preferable that the weight average molecular weight of the (A2)component as a whole is within a range of 800 to 100000. In this range,a liquid solder resist composition can achieve excellentphotosensitivity and resolution.

The acid value of the (A2) component as a whole is preferably 30 mgKOH/gor greater, and in this case, the liquid solder resist composition canbe easily developed. It is further preferable that this acid value is 60mgKOH/g or greater. Also, the acid value of the (A2) component as awhole is preferably 180 mgKOH/g or less, and in this case, a residualamount of carboxyl groups in a covering film made of the liquid solderresist composition is reduced, and good electrical properties,electrical corrosion-resistance, water-resistance, and the like of thecovering film are maintained. It is further preferable that the acidvalue is 150 mgKOH/g or less.

A photopolymerizable compound provides the liquid solder resistcomposition with photocurability. The photopolymerizable compoundcontains at least one compound selected from the group consisting ofphotopolymerizable monomers and photopolymerizable prepolymers.

The photopolymerizable monomer has an ethylene-based unsaturated group,for example. The photopolymerizable monomer can contain at least onecompound selected from the group consisting of monofunctional(meth)acrylates such as 2-hydroxyethyl (meth)acrylate; andpolyfunctional (meth)acrylates such as diethylene glycoldi(meth)acrylate, trimethylolpropane di(meth)acrylate,trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, andε-caprolactone modified pentaerythritol hexaacrylate, for example.

It is also preferable that the photopolymerizable monomer contains aphosphorus-containing compound (phosphorus-containing photopolymerizablecompound). In this case, a substance obtained by curing the liquidsolder resist composition has improved flame retardance. Thephosphorus-containing photopolymerizable compound can contain at leastone compound selected from the group consisting of2-methacryloyloxyethylacid phosphate (specific examples include partnumber “light ester P-1M” and “light ester P-2M” available from KyoeishaChemical Co., LTD.), 2-acryloyloxyethylacid phosphate (specific examplesinclude part number “light acrylate P-LA” available from KyoeishaChemical Co., LTD.), diphenyl-2-methacryloyloxyethyl phosphate (specificexamples include part number “MR-260” available from Daihachi ChemicalCo., LTD.), and HFA series available from Showa highpolymer Co., LTD.(specific examples include part number “HFA-6003” and “HFA-6007”, whichare products resulting from the addition reaction betweendipentaerythritol hexaacrylate and HCA, part number “HFA-3003” and“HFA-6127”, which are products resulting from the addition reactionbetween caprolactone modified dipentaerythritol hexaacrylate and HCA,and the like), for example.

Examples of photopolymerizable prepolymers include prepolymers obtainedby adding an ethylene-based unsaturated group to a prepolymer obtainedby polymerization of a photopolymerizable monomer, oligo (meth)acrylateprepolymers such as epoxy (meth)acrylate, polyester (meth)acrylate,urethane (meth)acrylate, alkyd resin (meth)acrylate, silicone resin(meth)acrylate, and spirane resin (meth)acrylate.

In the present embodiment, the photopolymerization initiator containsbisacylphosphine oxide-based photopolymerization initiator, a firstα-hydroxyalkyl phenone-based photopolymerization initiator, and a secondα-hydroxyalkyl phenone-based photopolymerization initiator. The firstα-hydroxyalkyl phenone-based photopolymerization initiator is a liquidat 25° C., and the second α-hydroxyalkyl phenone-basedphotopolymerization initiator is a solid at 25° C.

Thus, in the present embodiment, the solder resist layer obtained bycuring a coating film made of a liquid solder resist composition usingultraviolet rays can be sufficiently cured entirely from its upperportion to its lower portion. The reason is considered to be as follows.

The bisacylphosphine oxide-based photopolymerization initiator reactsusing a component of comparatively long-wavelength ultraviolet rays.Such a component of comparatively long-wavelength is likely to reach thelower portion of the coating film made of the liquid solder resistcomposition. Therefore, the bisacylphosphine oxide-basedphotopolymerization initiator can improve the efficiency of aphoto-curing reaction in the lower portion of the coating film.

On the other hand, the first α-hydroxyalkyl phenone-basedphotopolymerization initiator and the second α-hydroxyalkylphenone-based photopolymerization initiator react using a componenthaving comparatively short-wavelength ultraviolet rays. The componenthaving such comparatively short-wavelength ultraviolet rays is unlikelyto reach the lower portion of the coating film. However, the reactionsof the first α-hydroxyalkyl phenone-based photopolymerization initiatorand the second α-hydroxyalkyl phenone-based photopolymerizationinitiator are unlikely to be interfered by oxygen, and therefore havehigh photoreactivity. Therefore, the first α-hydroxyalkyl phenone-basedphotopolymerization initiator and the second α-hydroxyalkylphenone-based photopolymerization initiator can improve the efficiencyof a photo-curing reaction in the upper portion of the coating film.

Furthermore, because a light wavelength region in which the firstα-hydroxyalkyl phenone-based photopolymerization initiator undergoes areaction is different from a light wavelength region in which the secondα-hydroxyalkyl phenone-based photopolymerization initiator undergoes areaction, ultraviolet rays can be efficiently used. Therefore, thephoto-curing reaction further efficiently progresses in the upperportion of the coating film.

Accordingly, in the present embodiment, it is possible to allow thephoto-curing reaction to efficiently progress entirely from the upperportion of the coating film to the lower portion thereof. Accordingly,it is conceivable that the upper portion of the solder resist layer canbe sufficiently cured and the lower portion thereof can also besufficiently cured.

If the solder resist layer is sufficiently cured entirely from its upperportion to its lower portion, the degree of hardness of the solderresist layer is unlikely to have variations, as a result of whichwrinkles resulting from shrinkage during curing are unlikely to occur inthe solder resist layer. Accordingly, the solder resist layer has animproved smoothness.

Also, if the solder resist layer is sufficiently cured from its upperportion to its lower portion, the solder resist layer has an improvedhomogeneity. Therefore, even though stress occurs due to the solderresist layer being deformed by heat in soldering process, reflowingprocess, and the like, the stress is easily distributed in the solderresist layer, as a result of which cracks are unlikely to occur in thesolder resist layer.

Also, a bisacylphosphine oxide-based photopolymerization initiator isgenerally likely to be crystallized. If crystals of the bisacylphosphineoxide-based photopolymerization initiator are precipitated in the liquidsolder resist composition, there are risks that as a result of thecrystals rising to the surface of the coating film made of the liquidsolder resist composition, uniformity of the surface of the solderresist layer is deteriorated, reliability of a printed-wiring board isextremely reduced, and it is difficult for the liquid solder resistcomposition to be uniformly cured using ultraviolet rays. However, inthe present embodiment, the liquid solder resist composition containsthe first α-hydroxyalkyl phenone-based photopolymerization initiatorthat is a liquid at 25° C., and thereby crystals of the bisacylphosphineoxide-based photopolymerization initiator are inhibited from beingprecipitated even though the liquid solder resist composition is storedfor a long period of time. Furthermore, the liquid solder resistcomposition contains the second α-hydroxyalkyl phenone-basedphotopolymerization initiator that is a solid at 25° C., and thereby theeffects are especially obtained. Accordingly, the liquid solder resistcomposition has an improved storage stability.

Also, if the photopolymerization initiator contains only thebisacylphosphine oxide-based photopolymerization initiator and the firstα-hydroxyalkyl phenone-based photopolymerization initiator, the amountof the first α-hydroxyalkyl phenone-based photopolymerization initiatoris increased, and thus the tackiness of a coating film (dried coatingfilm) made of the liquid solder resist composition is increased.However, in the present embodiment, the photopolymerization initiatoralso contains the second α-hydroxyalkyl phenone-basedphotopolymerization initiator that is a solid at 25° C., and thereby theamount of the first α-hydroxyalkyl phenone-based photopolymerizationinitiator can be reduced, and the tackiness of the coating film can bereduced without losing a good storage stability. Thus, the coating filmcan be easily handled, and even though a negative mask or the like isarranged on the coating film when the coating film is exposed to light,the negative mask or the like is unlikely to be attached to the coatingfilm, as a result of which the workability is improved.

Also, the first α-hydroxyalkyl phenone-based photopolymerizationinitiator and the second α-hydroxyalkyl phenone-basedphotopolymerization initiator do not generate a benzyl radical at thetime of a photo-curing reaction, and therefore the solder resist layeris unlikely to be colored. Furthermore, although the bisacylphosphineoxide-based photopolymerization initiator naturally has a color,bleaching occurs due to decomposition at the time of the photo-curingreaction, as a result of which the solder resist layer is unlikely to becolored. Thus, the solder resist layer is inhibited from turning yellow,whiteness of the solder resist layer is increased, and the good lightreflectivity of the solder resist layer can be maintained.

The bisacylphosphine oxide-based photopolymerization initiator cancontain at least one component selected from the group consisting of

-   bis-(2,6-dichlorobenzoyl)phenylphosphine oxide,-   bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenyl phosphine oxide,-   bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide,-   bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide,-   bis-(2,6-dimethoxybenzoyl)phenylphosphine oxide,-   bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,-   bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, and-   bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide,    for example. In particular, the bisacylphosphine oxide-based    photopolymerization initiator preferably contains    bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and more    preferably contains only bis-(2,4,6-trimethylbenzoyl)phenylphosphine    oxide. In these cases, the solder resist layer is further inhibited    from being colored.

The melting point of the first α-hydroxyalkyl phenone-basedphotopolymerization initiator is particularly preferably within a rangeof −40 to 25° C., and further preferably within a range of 0 to 20° C.The first α-hydroxyalkyl phenone-based photopolymerization initiator cancontain at least one of 2-hydroxy-2-methyl-1-phenyl-propane-1-one andphenylglyoxylic acid methyl ester, for example. In particular, the firstα-hydroxyalkyl phenone-based photopolymerization initiator preferablycontains 2-hydroxy-2-methyl-1-phenyl-propane-1-one, and also preferablycontains only 2-hydroxy-2-methyl-1-phenyl-propane-1-one. In these cases,the solder resist layer is further inhibited from being colored.

The melting point of the second α-hydroxyalkyl phenone-basedphotopolymerization initiator is particularly preferably within a rangeof 25 to 200° C., and further preferably within a range of 40 to 100° C.The second α-hydroxyalkyl phenone-based photopolymerization initiatorcan contain at least one component selected from the group consisting of1-hydroxycyclohexyl phenyl ketone,1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, and2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propane-1-one.In particular, the second α-hydroxyalkyl phenone-basedphotopolymerization initiator preferably contains 1-hydroxycyclohexylphenyl ketone, and also preferably contains only 1-hydroxycyclohexylphenyl ketone. In these cases, the solder resist layer is furtherinhibited from being colored.

It is preferable that the mass ratio of the bisacylphosphine oxide-basedphotopolymerization initiator and the first α-hydroxyalkyl phenone-basedphotopolymerization initiator is within a range of 1:0.5 to 1:5. If themass ratio of the first α-hydroxyalkyl phenone-based photopolymerizationinitiator relative to the bisacylphosphine oxide-basedphotopolymerization initiator is 0.5 or greater, the bisacylphosphineoxide-based photopolymerization initiator is particularly inhibited frombeing crystallized in the liquid solder resist composition, as a resultof which the storage stability of the liquid solder resist compositionis increased in particular. Also, if the mass ratio of the firstα-hydroxyalkyl phenone-based photopolymerization initiator relative tothe bisacylphosphine oxide-based photopolymerization initiator is 5 orless, the tackiness of the coating film (dried coating film) is reducedin particular. It is further preferable that the mass ratio is within arange of 1:1 to 1:4.

It is preferable that the mass ratio of the bisacylphosphine oxide-basedphotopolymerization initiator and the second α-hydroxyalkylphenone-based photopolymerization initiator is within a range of 1:0.5to 1:5. If the mass ratio of the second α-hydroxyalkyl phenone-basedphotopolymerization initiator relative to the bisacylphosphineoxide-based photopolymerization initiator is 0.5 or greater, dissolutionof the bisacylphosphine oxide-based photopolymerization initiator in theliquid solder resist composition is particularly facilitated, as aresult of which the storage stability of the liquid solder resistcomposition is increased in particular. Also, if the mass ratio of thesecond α-hydroxyalkyl phenone-based photopolymerization initiatorrelative to the bisacylphosphine oxide-based photopolymerizationinitiator is 5 or less, the lower portion of the solder resist layer hasincreased curability. It is further preferable that the mass ratio iswithin a range of 1:1 to 1:4.

The liquid solder resist composition may further contain a knownphotopolymerization accelerating agent, a sensitizer, and the like. Forexample, the liquid solder resist composition may containp-dimethylbenzoic acid ethyl ester, p-dimethylaminobenzoic acid isoamylester, 2-dimethylaminoethyl benzoate, and the like.

It is preferable that the photopolymerization initiator contains onlythe bisacylphosphine oxide-based photopolymerization initiator, thefirst α-hydroxyalkyl phenone-based photopolymerization initiator, andthe second α-hydroxyalkyl phenone-based photopolymerization initiator.However, the photopolymerization initiator can also contain a componentother than three types of the components described above withoutdeparting from the gist of the present invention. For example, inaddition to the three types of the components described above, thephotopolymerization initiator may contain at least one componentselected from the group consisting of benzoin and alkyl ethers thereof;acetophenones such as acetophenone and benzyl dimethyl ketal;anthraquinones such as 2-methylanthraquinone; thioxanthones such as2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,2-isopropyithioxanthone, 4-isopropylthioxanthone, and2,4-diisopropylthioxanthone; benzophenones such as benzophenone and4-benzoyl-4′-methyldiphenyl sulfide; xanthones such as 2,4-diisopropylxanthone; compounds containing a nitrogen atom, such as2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone;monoacylphosphine oxide-based photopolymerization initiators such as2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (DAROCUR TPO) and2,4,6-trimethylbenzoyl-ethyl-phenyl-phosphinate (SPEEDCURE TPO-L);1,2-octane-dione, 1-[4-(phenylthio)-2-(O-benzoyloxime)] (IRGACURE OXE01), ethanone and1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-1-(O-acetyl oxime)(IRGACURE OXE 02).

Titanium dioxide turns the solder resist layer made of the liquid solderresist composition into white, as a result of which it provides thesolder resist layer with a high light reflectivity. In the presentembodiment, the titanium dioxide contains both of a rutile titaniumdioxide manufactured by a sulfuric acid method and a rutile titaniumdioxide manufactured by a chlorine method. In a case where only one ofthe rutile titanium oxides manufactured by the sulfuric acid method orthe chlorine method is used, light reflectivity of the solder resistlayer may decrease and the solder resist layer may turn its color toyellow due to the ultraviolet rays. However, in a case where the liquidsolder resist layer contains both of the rutile titanium dioxidesmanufactured by two kinds of methods, as in the present embodiment,these two kinds of the rutile titanium oxides can supplement eachother's shortcoming with each other's advantage. Therefore, the solderresist layer that has high reflectivity with suppressed deteriorationespecially due to light can be formed. In other words, since the solderresist layer contains the rutile titanium oxides manufactured by thesulfuric acid method, discoloration such as yellowing of the solderresist layer can be suppressed even if the solder resist layer isirradiated with ultraviolet rays. Moreover, since the solder resistlayer contains the rutile titanium oxides manufactured by the chlorinemethod, b* value in an L*a*b* colorimetric system of the solder resistlayer becomes small, which turns the color of the solder resist layerbluish. Due to this, the solder resist layer is likely to be visuallyrecognized as white and thus may have high reflectivity.

The liquid solder resist composition can be made into a thermoset by thecompound having a cyclic ether skeleton.

It is particularly preferable that the compound having a cyclic etherskeleton contains an epoxy compound. The compound having a cyclic etherskeleton may be a compound having an oxetane ring.

It is preferable that the epoxy compound has at least two epoxy groupsin one molecule. The epoxy compound may be a solvent-insoluble epoxycompound, or a general solvent-soluble epoxy compound. There is noparticular limitation on the types of epoxy compounds, and inparticular, it is preferable that the epoxy compound contains at leastone component selected from the group consisting of phenol novolac epoxyresins (specific examples include part number “EPICLON N-775” availablefrom DIC Corporation), cresol novolac epoxy resins (specific examplesinclude part number “EPICLON N-695” available from DIC Corporation),bisphenol A epoxy resin (specific examples include part number “jER1001”available from Mitsubishi Chemical Corporation), bisphenol A-novolacepoxy resins (specific examples include part number “EPICLON N-865”available from DIC Corporation), bisphenol F epoxy resins (specificexamples include part number “jER4004P” available from MitsubishiChemical Corporation), bisphenol S epoxy resins (specific examplesinclude part number “EPICLON EXA-1514” available from DIC Corporation),bisphenol AD epoxy resins, biphenyl epoxy resins (specific examplesinclude part number “YX4000” available from Mitsubishi ChemicalCorporation), biphenyl novolac epoxy resins (specific examples includepart number “NC-3000” available from Nippon Kayaku Co., Ltd.),hydrogenated bisphenol A epoxy resins (specific examples include partnumber “ST-4000D” available from Nippon Steel & Sumikin Chemical Co.,Ltd.), naphthalene epoxy resins (specific examples include part number“EPICLON HP-4032”, “EPICLON HP-4700”, and “EPICLON HP-4770” availablefrom DIC Corporation), hydroquinone-type epoxy resins (specific examplesinclude part number “YDC-1312” available from Nippon Steel & SumikinChemical Co., Ltd.), tertiary butylcatechol-type epoxy resins (specificexamples include part number “EPICLON HP-820” available from DICCorporation), dicyclopentadiene type epoxy resins (specific examplesinclude part number “EPICLON HP-7200” available from DIC Corporation),adamantane-type epoxy resins (specific examples include part number“ADAMANTATE X-E-201” available from Idemitsu Kosan Co., Ltd.), biphenylether type epoxy resins (specific examples include part number“YSLV-80DE” available from Nippon Steel & Sumikin Chemical Co., Ltd.),unique bifunctional epoxy resins (specific examples include part number“YL7175-500” and “YL7175-1000” available from Mitsubishi ChemicalCorporation; part number “EPICLON TSR-960”, “EPICLON TER-601”, “EPICLONTSR-250-80BX”, “EPICLON 1650-75MPX”, “EPICLON EXA-4850”, “EPICLONEXA-4816”, “EPICLON EXA-4822”, and “EPICLON EXA-9726” available from DICCorporation; part number “YSLV-120TE” available from Nippon Steel &Sumikin Chemical Co., Ltd.), and bisphenol-based epoxy resins other thanthe epoxy resins described above.

It is also preferable that the epoxy compound contains triglycidylisocyanurate. As triglycidyl isocyanurate, a β form having three epoxygroups oriented in the same direction relative to a plane of anS-triazine ring skeleton is particularly preferable, and alternatively,a mixture of this β form and an α form that has a structure in which oneepoxy group is oriented, relative to a plane of the S-triazine ringskeleton, in a different direction from the direction in which the othertwo epoxy groups are oriented relative to the plane thereof ispreferable.

It is also preferable that the epoxy compound contains aphosphorus-containing epoxy resin. In this case, a substance obtained bycuring the liquid solder resist composition has an improvedincombustibility. Examples of the phosphorus-containing epoxy resinsinclude a phosphoric acid modified bisphenol F epoxy resin (specificexamples include part number “EPICRON EXA-9726” and “EPICLON EXA-9710”available from DIC Corporation) and part number “epotohto FX-305”available from Nippon Steel & Sumikin Chemical Co., Ltd.

The liquid solder resist composition may contain an organic solvent. Theorganic solvent is used for liquefying or varnishing the liquid solderresist composition, and adjusting the viscosity, application properties,and film formation properties of the liquid solder resist composition,and the like.

The organic solvent can contain at least one compound selected from thegroup consisting of linear, branched, secondary, or polyhydric alcoholssuch as ethanol, propyl alcohol, isopropyl alcohol, hexanol, andethylene glycol; ketones such as methyl ethyl ketone and cyclohexanone;aromatic hydrocarbons such as toluene and xylene; petroleum-basedaromatic mixed solvent such as Swazole series (available from MaruzenPetrochemical Co., Ltd.), Solvesso series (available from Exxon ChemicalCo.); cellosolves such as cellosolve and butyl cellosolve; carbitolssuch as carbitol and butyl carbitol; propylene glycol alkyl ethers suchas propylene glycol methyl ether; polypropylene glycol alkyl ethers suchas dipropylene glycol methyl ether, acetic esters such as ethyl acetate,butyl acetate, cellosolve acetate, and carbitol acetate; and dialkylglycol ethers, for example.

It is preferable that the ratio of the organic solvent in the liquidsolder resist composition is adjusted such that the organic solvent isquickly volatilized when a coating film made of the liquid solder resistcomposition is dried, or in other words, such that the dried film doesnot contain the organic solvent. In particular, the organic solvent ispreferably within a range of 0 to 99.5% by mass relative to the liquidsolder resist composition as a whole, and further preferably within arange of 15 to 60% by mass. It should be noted that it is preferablethat the ratio is appropriately adjusted in accordance with anapplication method because a preferred ratio of the organic solvent isdifferent in accordance with an application method, or the like.

The liquid solder resist composition may further contain a componentother than the above-described components without departing from thegist of the present invention.

For example, the liquid solder resist composition may contain at leastone resin selected from the group consisting of tolylenediisocyanate-based, morpholine diisocyanate-based, isophoronediisocyanate-based, and hexamethylene diisocyanate-based blockedisocyanates that are blocked with caprolactam, oximes, malonic esters,or the like; amino resins such as melamine resins, n-butylated melamineresins, isobutylated melamine resins, butylated urea resins, butylatedmelamine-urea co-condensation resins, and benzoguanamine-basedco-condensation resins; various types of thermosetting resins other thanthe above-described resins; ultraviolet-curable epoxy (meth)acrylate;resins obtained by adding (meth)acrylic acid to an epoxy resin such asbisphenol A, phenol novolac, cresol novolac, alicyclic or the likeresin; and macromolecular compounds such as diallyl phthalate resins,phenoxy resins, urethane resins, and fluororesins.

In the case where the liquid solder resist composition contains an epoxycompound, the liquid solder resist composition may further contain acuring agent for curing the epoxy compound. The curing agent can containat least one component selected from the group consisting of imidazolederivatives such as imidazole, 2-methylimidazole, 2-ethylimidazole,2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole,1-cyanoethyl-2-phenylimidazole, and1-(2-cyanoethyl)-2-ethyl-4-methylimidazole; amine compounds such asdicyandiamide, benzyldimethylamine,4-(dimethylamino)-N,N-dimethylbenzylamine,4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine;hydrazine compounds such as adipic acid hydrazide and sebacic acidhydrazide; phosphorus compounds such as triphenylphosphine; acidanhydrides; phenol; mercaptan; Lewis acid amine complexes; and oniumsalts, for example. Examples of commercial products of these componentsinclude 2MZ-A, 2MZ-OK, 2PHZ, 2P4BHZ, and 2P4MHZ (they are product namesof imidazole-based compounds) available from Shikoku ChemicalsCorporation, U-CAT3503N and U-CAT3502T (they are product names ofblocked isocyanate compounds of dimethylamine), and DBU, DBN,U-CATSA102, and U-CAT5002 (they are bicyclic amidine compounds and saltsthereof) available from San-Apro Ltd.

The liquid solder resist composition may contain an adhesion impartingagent. Examples of the adhesion imparting agent include guanamine,acetoguanamine, benzoguanamine, melamine, and S-triazine derivativessuch as 2,4-diamino-6-methacryloyloxyethyl-S-triazine,2-vinyl-4,6-diamino-S-triazine,2-vinyl-4,6-diamino-S-triazine/isocyanuric acid adducts, and2,4-diamino-6-methacryloyloxyethyl-S-triazine/isocyanuric acid adducts.

The liquid solder resist composition may contain at least one componentselected from the group consisting of hardeners; coloring agents otherthan white color; copolymers such as silicone and acrylates; levelingagents; adhesion imparting agents such as silane coupling agents;thixotropy agents; polymerization inhibitors; antihalation agents; flameretardants; antifoaming agents; antioxidants; surfactants; macromoleculedispersants; and inorganic fillers such as barium sulfate, crystallinesilica, nanosilica, carbon nanotubes, talc, bentonite, aluminumhydroxide, and magnesium hydroxide.

Respective amounts of the components of the liquid solder resistcomposition are appropriately adjusted such that the liquid solderresist composition has photocurability and can be developed using analkaline solution.

The percentage of the carboxyl group-containing resin is preferablywithin a range of 5 to 85% by mass relative to the solid componentamount of the liquid solder resist composition, more preferably within arange of 10 to 75% by mass, and further preferably within a range of 10to 40% by mass.

The percentage of the photopolymerizable compound is preferably within arange of 1 to 45% by mass relative to the solid component amount of theliquid solder resist composition, more preferably within a range of 2 to40% by mass, and further preferably within a range of 5 to 30% by mass.

Also, the percentage of the compound having a cyclic ether skeleton ispreferably within a range of 1.5 to 85% by mass relative to the solidcomponent amount of the liquid solder resist composition, morepreferably within a range of 1.5 to 65% by mass, and further preferablywithin a range of 2 to 40% by mass.

The percentage of the photopolymerization initiator is preferably withina range of 0.1 to 30% by mass relative to the solid component amount ofthe liquid solder resist composition, and further preferably within arange of 1 to 28% by mass.

Preferable contents of two kinds of the titanium dioxides in the liquidsolder resist composition are as follows. It is preferable that relativeto 100 parts by mass of a total of the carboxyl group-containing resin,the photopolymerizable compound, and the compound having a cyclic etherskeleton, the rutile titanium dioxide manufactured by the sulfuric acidmethod is within a range of 30 to 400 parts by mass and the rutiletitanium dioxide manufactured by the chlorine method is larger than orequal to 5 parts by mass and less than 50 parts by mass. In this case,light reflectivity of the solder resist layer can be further improvedand deterioration due to ultraviolet rays can be further suppressed.

It should be noted that the solid component amount refers to the totalamount of all components from which components of solvents and the likethat volatilize in the process for forming the solder resist layer fromthe liquid solder resist composition are removed.

Raw materials for the liquid solder resist composition described abovecan be mixed and kneaded by a known kneading method using, for example,a three roll mill, a ball mill, or a sand mill to prepare the liquidsolder resist composition.

Taking storage stability and the like into consideration, a portion ofraw materials for the liquid solder resist composition may be mixed toprepare a first agent, and then a remaining portion of the raw materialsmay be mixed to prepare a second agent. In other words, the liquidsolder resist composition may contain the first agent and the secondagent. For example, the photopolymerizable compound, the compound havinga cyclic ether skeleton and a portion of the organic solvent, of the rawmaterials, may be mixed and dispersed in advance to prepare the firstagent. Also, the remaining portion of the raw materials may be mixed anddispersed to prepare the second agent. In this case, an appropriaterequired amount of the first and second agents are mixed at anappropriate time to prepare a liquid mixture, and then the solder resistlayer can be formed using this liquid mixture.

The liquid solder resist composition according to the present embodimentis applied for forming the solder resist layer on a printed-wiringboard, for example.

Hereinafter, an example of methods for forming the solder resist layeron a printed-wiring board using the liquid solder resist compositionaccording to the present embodiment will be described. In this example,the solder resist layer is formed using a photocurable and thermosettingliquid solder resist composition.

First, a printed-wiring board is prepared, and the liquid solder resistcomposition is used to form a coating film on the printed-wiring board.For example, the liquid solder resist composition is applied onto thesurface of the printed-wiring board to form a wet-state coating film(wet coating film). A method for applying the liquid solder resistcomposition can be selected from the group consisting of known methods,for example, dipping, spraying, spin coating, roll coating, curtaincoating, and screen printing methods. Thereafter, in order to volatilizethe organic solvent in the liquid solder resist composition as needed,the wet coating film is dried under a temperature within a range of 60to 120° C., for example, to obtain a post-dried coating film (driedcoating film). In the present embodiment, as a result of thephotopolymerization initiator containing three types of components asdescribed above, the tackiness of the dried coating film is suppressed.

It should be noted that when the coating film is formed on theprinted-wiring board, it is possible to adopt the following method(dried film method) that: the liquid solder resist composition isapplied onto an appropriate support body and then dried to obtain thedried coating film in advance; this dried coating film is placed on theprinted-wiring board; and then pressure is applied to the dried coatingfilm and the printed-wiring board to provide the dried coating film onthe printed-wiring board.

Thereafter, a negative mask is directly or indirectly applied to thedried coating film on the printed-wiring board, and then the negativemask is irradiated with active energy rays, as a result of which thecoating film is exposed to light via the negative mask. The negativemask includes an exposure portion that allows the active energy rays topass through and a non-exposure portion that blocks the active energyrays, and the exposure portion has a shape that matches the pattern ofthe solder resist layer. A photo tool such as a mask film or a dry plateis used as the negative mask. The active energy rays are selected inaccordance with the composition of the liquid solder resist composition,and in the present embodiment, ultraviolet rays are used. The lightsource for the ultraviolet rays is selected from the group consisting ofa chemical lamp, a low pressure mercury lamp, a medium pressure mercurylamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp,a xenon lamp, and a metal halide lamp.

It should be noted that a method other than the method using thenegative mask may be adopted as an exposure method. For example, adirect drawing method by means of laser exposure or the like may beadopted.

In the present embodiment, if the dried coating film is exposed toultraviolet rays in this manner, as described above, a photo-curingreaction efficiently progresses entirely from the upper portion of thedried coating film to the lower portion thereof.

After the dried coating film is exposed to light, the negative mask isremoved from the printed-wiring board, and then a development treatmentis performed on the dried coating film to remove a portion of the driedcoating film that is not exposed to light. As a result, the portion ofthe dried coating film that was exposed to light remains on a firstsurface and a second surface of the printed-wiring board as the solderresist layer.

In the development treatment, an appropriate developer can be used inaccordance with the composition of the liquid solder resist composition.Specific examples of developers include alkaline solutions such as anaqueous sodium carbonate solution, aqueous potassium carbonate solution,aqueous ammonium carbonate solution, aqueous sodium bicarbonatesolution, aqueous potassium bicarbonate solution, aqueous ammoniumbicarbonate solution, aqueous sodium hydroxide solution, aqueouspotassium hydroxide solution, aqueous ammonium hydroxide solution,aqueous tetramethyl ammonium hydroxide solution, and aqueous lithiumhydroxide solution. Organic amines such as monoethanolamine,diethanolamine, triethanolamine, monoisopropanolamine,diisopropanolamine, and triisopropanolamine can also be used as thedeveloper. These developers can be used alone or in combination. In thecase where the developer is an alkaline solution, the solvent thereofmay be only water, or a mixture of water and a hydrophilic organicsolvent such as lower alcohols.

The solder resist layer may be heat-cured by performing a heat treatmenton the solder resist layer as needed. The conditions for the heattreatment are within a range of a heating temperature of 120 to 180° C.and within a range of a heating time of 30 to 90 minutes, for example.Accordingly, the performance of the solder resist layer, such as thestrength, hardness, and chemical resistance, is improved.

Also, after the heat treatment was performed on the solder resist layer,the solder resist layer may be further irradiated with ultraviolet raysas needed. In this case, it is possible to further advance thephoto-curing reaction in the solder resist layer. Accordingly, themigration resistance of the solder resist layer is further improved.

As described above, a covered-printed wiring board that includes theprinted-wiring board and the solder resist layer that partially coversthe printed-wiring board can be obtained. In the present embodiment, thesolder resist layer is sufficiently cured entirely from its upperportion to its lower portion. Furthermore, since the solder resist layercontains two kinds of the rutile titanium dioxides manufactured by thesulfuric acid method and the chlorine method, the solder resist layerhas high reflectivity and deterioration of the solder resist layer dueto light and heat is suppressed.

Example

Hereinafter, an example of the present invention will be described.However, the present invention is not limited to the example describedbelow.

[Preparation of Base Resin Solution (Saturated)]

A base resin solution (saturated) containing a carboxyl group-containingresin was prepared as follows.

42 parts by mass of methacrylic acid, 118 parts by mass of methylmethacrylate, 20 parts by mass of N-phenylmaleimide, 20 parts by mass ofbutyl methacrylate, 320 parts by mass of dipropylene glycol monomethylether, and 5 parts by mass of azobisisobutyronitrile were placed in afour-neck flask into which a reflux condenser, a thermometer, a glasstube for nitrogen substitution, and a stirrer were inserted. The liquidin this four-neck flask was heated at 75° C. for 5 hours under nitrogengas stream to advance a polymerization reaction, as a result of which acopolymer solution having a concentration of 38% was obtained.

[Preparation of Base Resin Solution (Unsaturated)]

A base resin solution (unsaturated) containing a carboxylgroup-containing resin was prepared as follows.

60 parts by mass of methacrylic acid, 50 parts by mass ofω-carboxy-polycaprolactone (n≈2) monoacrylate (ARONIX M-5300 availablefrom Toagosei Co., LTD.), 80 parts by mass of methyl methacrylate, 10parts by mass of styrene, 430 parts by mass of dipropylene glycolmonomethyl ether, and 5 parts by mass of azobisisobutyronitrile wereplaced in a four-neck flask into which a reflux condenser, athermometer, a glass tube for nitrogen substitution, and a stirrer wereinserted. The liquid in this four-neck flask was heated at 75° C. for 5hours under nitrogen gas stream to advance a polymerization reaction, asa result of which a copolymer solution having a concentration of 32% wasobtained.

0.1 parts by mass of hydroquinone, 64 parts by mass ofglycidylmethacrylate, and 0.8 parts by mass of dimethylbenzylamine wereadded to this copolymer solution, and the mixture was heated at 80° C.for 24 hours to advance an addition reaction. Accordingly, a 38%solution of a compound having a carboxyl group and an ethylene-basedunsaturated group was obtained.

[Preparation of Liquid Solder Resist Compositions]

Liquid solder resist compositions were each obtained by mixingcomponents in accordance with an item in Tables below and kneaded usinga three roll mill. It should be noted that the details of the componentsshown in Table are as follows.

-   -   Photopolymerization initiator (IRGACURE819);        bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, available        from BASF SE, part number “IRGACURE819”.    -   Photopolymerization initiator (IRGACURE184);        1-hydroxy-cyclohexyl-phenyl-ketone, available from BASF SE, part        number “IRGACURE184”.    -   Photopolymerization initiator (DAROCUR 1173);        2-hydroxy-2-methyl-1-phenyl-propane-1-one, available from BASF        SE, part number “DAROCUR 1173”.    -   Rutile titanium dioxide R-79; a rutile titanium dioxide        manufactured by the sulfuric acid method, available from Sakai        Chemical Industry Co., Ltd., part number “R-79”.    -   Rutile titanium dioxide D-918; a rutile titanium dioxide        manufactured by the sulfuric acid method, available from Sakai        Chemical Industry Co., Ltd., part number “D-918”.    -   Rutile titanium dioxide CR-90; a rutile titanium dioxide        manufactured by the chlorine method, available from Ishihara        Sangyo Kaisha, LTD, part number “CR-90”.    -   Rutile titanium dioxide CR-58; a rutile titanium dioxide        manufactured by the chlorine method, available from Ishihara        Sangyo Kaisha, LTD, part number “CR-58”.    -   Anatase titanium dioxide A-100; available from Ishihara Sangyo        Kaisha, LTD, part number “A-100”.    -   Epoxy compound; available from Nissan Chemical Industries, Ltd.,        part number “TEPIC-SP”.    -   Organic solvent; Methyl Propylene Di Glycol, available from        Nippon Nyukazai Co., Ltd., part number “MFDG”.    -   Photopolymerizable monomer; available from Nippon Kayaku Co.,        Ltd., part number “KAYARAD DPCA-20”.    -   Antifoaming agent; available from Shin-Etsu Chemical Co., Ltd.,        part number “KS-66”.    -   Melamine; available from Nissan Chemical Industries, Ltd., fine        powder melamine.    -   Antioxidant; available from BASF SE, part number “IRGANOX 1010”.

[Evaluation Test]

(1) Production of Test Pieces

A glass epoxy copper clad laminate that includes a copper foil having athickness of 35 μm was prepared. Etching was performed on this glassepoxy copper clad laminate to form conductive wiring, as a result ofwhich a printed-wiring board was obtained. A liquid solder resist resincomposition was applied to the entire surface of the printed-wiringboard by screen printing, as a result of which a coating film wasformed. This coating film was heated at 80° C. for 20 minutes to bedried. The thickness of a coating film obtained after drying the coatingfilm (dried coating film) was 20 μm. While a negative mask was directlyapplied to the surface of the dried coating film, the negative mask wasirradiated with ultraviolet rays so that the dried coating film wasselectively exposed to light under the condition of an exposure energyof 450 mJ/cm². Subsequently, after the negative mask was removed fromthe dried coating film, the development treatment was performed on thedried coating film using an aqueous sodium carbonate solution, as aresult of which a portion of the dried coating film that was cured bylight exposure was left on the printed-wiring board as a solder resistlayer. This solder resist layer was further heated at 150° C. for 60minutes to be cured by heat. According to such procedures, test pieces 1that each included the solder resist layer with thickness of 20 μm wereobtained. Besides, the liquid solder resist resin composition wasapplied by screen printing on a surface of the dried coating film ofanother printed wiring board before the above ultraviolet raysirradiation, as a result of which a coating film was formed. The coatingfilm was dried by heating for 20 minutes at 80° C. The post-driedcoating film (dried coating film) had a thickness of 40 μm. Similarprocesses as described above but with a different exposure energy of 600mJ/cm² were performed thereon, as a result of which test pieces 2 thateach included the solder resist layer with thickness of 40 μm wereobtained.

The following evaluation tests were performed on these test pieces 1, 2.

(2) Evaluation of Adhesion

In accordance with a test method of JIS D0202, a cross-cut was made intothe solder resist layer of each test piece 1, and then the peeled stateafter a peeling test using the cellophane adhesive tape was visuallyobserved. The results were evaluated as follows.

A: there was no change in all of the 100 cross-cut portions.

B: there was a slight raise in one portion among the 100 cross-cutportions.

C: there was peeling from 2 to 10 portions among the 100 cross-cutportions.

D: there was peeling from 11 to 100 portions among the 100 cross-cutportions.

(3) Pencil Hardness

The pencil hardness of the solder resist layer of each test piece 1 wasmeasured using a Mitsubishi Hi-uni pencil (available from MitsubishiPencil Co., Ltd.) in accordance with JIS K5400.

(4) Evaluation of Reflectivity

Y value in an CIE colorimetric system, which expresses a luminousreflectance, of the solder resist layer of each test piece 1 and testpiece 2 before a discoloration test was measured using aspectrophotometer (model number “CM-600d”) available from Konica MinoltaSensing, Inc. Then, after the discoloration test was carried out byirradiating the solder resist layer of each test piece 1 and test piece2 with ultraviolet rays (UV) under the condition of 50 J/cm², Y value ofthe solder resist layer was again measured using the same method asabove.

(5) Evaluation of Yellowing Resistance Due to Ultraviolet Rays

b* value in an L*a*b* colorimetric system of the solder resist layer ofeach test piece 1 and test piece 2 before a discoloration test wasmeasured using a spectrophotometer (model number “CM-600d”) availablefrom Konica Minolta Sensing, Inc. Then, after the discoloration test wascarried out by irradiating the solder resist layer of each test piece 1and test piece 2 with ultraviolet rays (UV) under the condition of 50J/cm², b* value of the solder resist layer was again measured using thesame method as above. A value (Δb*) was calculated by subtracting the b*value of the solder resist layer before the UV irradiation from the b*value of the solder resist layer after the UV irradiation. In addition,a surface of the solder resist layer after the UV irradiation wasvisually observed and the results were evaluated as follows.

A: there was no particularly large change in luster on the surface ofthe solder resist layer.

B: there was a slight decrease in luster on the surface of the solderresist layer.

C: there was no luster on the surface of the solder resist layer.

TABLE 1 Examples Comperative Examples 1 2 3 4 5 6 7 8 9 10 1 2 3 4Composition/ base resin solution (saturated) 100 100 100 100 100 100 100100 100 100 100 100 parts by mass base resin solution (unsaturated) 100100 photopolymerization initiator 5 5 6 5 4 5 6 5 4 4 5 5 5 5(IRGACURE819) photopolymerization initiator 8 8 5 8 6 8 5 8 6 6 8 8 8 8(IRGACURE184) photopolymerization initiator 13 13 12 13 10 13 12 13 1010 13 13 13 13 (DAROCUR1173) titanium dioxide (R-79) 85 70 55 55 55 115145 70 55 100 titanium dioxide (D-918) 55 titanium dioxide (CR-90) 15 3045 45 45 45 15 30 45 45 100 titanium dioxide (CR-58) 100 titaniumdioxide (A-100) 100 epoxy compound 10 10 10 10 10 10 10 10 10 10 10 1010 10 organic solvent 10 10 10 10 10 20 20 5 5 10 10 10 10 10photopolymerizable 30 30 30 30 30 40 40 20 20 30 30 30 30 30 monomer(DPCA-20) antifoaming agent 1 1 1 1 1 1 1 1 1 1 1 1 1 1 melamine 2 2 2 22 2 2 2 2 2 2 2 2 2 antioxidant 1 1 1 1 1 1 1 1 1 1 1 1 1 1 adhesion A AA A A A A A A A A A A A pencil hardness 5H 5H 5H 5H 5H 5H 5H 5H 5H 5H 5H5H 5H 5H reflectivity (Y value) before the 85 85 85 85 85 86 85 85 85 8583 85 75 82 discoloration test (%) (20 μm) reflectivity (Y value) afterthe 84 84 84 84 84 85 84 84 84 85 82 83 65 80 discoloration test (%) (UVirradiation) (20 μm) b* value before the discoloration 2 2 1.9 1.9 1.9 22.1 2 1.9 2.5 2.6 1.9 3 1.7 test (20 μm) Δb* after the discolorationtest 0.6 0.6 0.7 0.7 0.7 0.6 0.6 0.6 0.7 0.3 0.7 1.0 10 1.2 (UVirradiation) (20 μm) visual evaluation after the A A A A A A A A A A A BC B discoloration test (UV irradiation) (20 μm) reflectivity (Y value)before the 90 90 90 90 90 90 90 90 90 90 88 90 79 85 discoloration test(%) (40 μm) reflectivity (Y value) after the 88 88 88 88 88 88 88 88 8889 86 86 68 80 discoloration test (%) (UV irradiation) (40 μm) b* valuebefore the discoloration 2.3 2.3 2.2 2.2 2.2 2.3 2.4 2.3 2.2 2.8 3 2.23.3 1.9 test (40 μm) Δb* after the discoloration test 0.7 0.7 0.8 0.80.8 0.7 0.7 0.7 0.8 0.4 0.7 2.2 12 2.8 (UV irradiation) (40 μm) visualevaluation after the A A A A A A A A A A A B C B discoloration test (UVirradiation) (40 μm)

The invention claimed is:
 1. A liquid solder resist compositioncomprising: a carboxyl group-containing resin; a photopolymerizablecompound containing at least one compound selected from a groupconsisting of a photopolymerizable monomer and a photopolymerizableprepolymer; a photopolymerization initiator; a titanium dioxide; and acompound having a cyclic ether skeleton, the titanium dioxide containingboth of a rutile titanium dioxide manufactured by a sulfuric acid methodand a rutile titanium dioxide manufactured by a chlorine method, therutile titanium dioxide manufactured by the sulfuric acid method beingwithin a range of 30 to 400 parts by mass relative to 100 parts by massof a total of the carboxyl group-containing resin, thephotopolymerizable compound, and the compound having a cyclic etherskeleton, and the rutile titanium dioxide manufactured by the chlorinemethod being larger than or equal to 5 parts by mass and less than 50parts by mass, relative to 100 parts by mass of a total of the carboxylgroup-containing resin, the photopolymerizable compound, and thecompound having a cyclic ether skeleton.
 2. The liquid solder resistcomposition according to claim 1, wherein the photopolymerizationinitiator contains a bisacylphosphine oxide-containingphotopolymerization initiator, a first α-hydroxyalkyl phenone-containingphotopolymerization initiator, and a second α-hydroxyalkylphenone-containing photopolymerization initiator.
 3. The liquid solderresist composition according to claim 2, wherein: the bisacylphosphineoxide-containing photopolymerization initiator containsbis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide; the firstα-hydroxyalkyl phenone-containing photopolymerization initiator contains2-hydroxy-2-methyl-1-phenyl-propane-1-one; and the second α-hydroxyalkylphenone-containing photopolymerization initiator contains1-hydroxycyclohexyl phenyl ketone.
 4. The liquid solder resistcomposition according to claim 2, wherein a mass ratio of thebisacylphosphine oxide-containing photopolymerization initiator and thefirst α-hydroxyalkyl phenone-containing photopolymerization initiator iswithin a range of 1:0.5 to 1:5.
 5. The liquid solder resist compositionaccording to claim 2, wherein a mass ratio of the bisacylphosphineoxide-containing photopolymerization initiator and the secondα-hydroxyalkyl phenone-containing photopolymerization initiator iswithin a range of 1:0.5 to 1:5.
 6. The liquid solder resist compositionaccording to claim 1, wherein the carboxyl group-containing resincontains a photopolymerizable carboxyl group-containing resin having acarboxyl group and a photopolymerizable functional group.
 7. The liquidsolder resist composition according to claim 6, wherein thephotopolymerizable carboxyl group-containing resin contains a carboxylgroup-containing (meth)acrylic copolymer resin.
 8. A covered-printedwiring board, comprising a printed-wiring board and a solder resistlayer that covers the printed-wiring board, wherein the solder resistlayer is made of the liquid solder resist composition according toclaim
 1. 9. The liquid solder resist composition according to claim 1,wherein: a percentage of the carboxyl group-containing resin is within arange of 5 to 85% by mass relative to a solid component amount of theliquid solder resist composition; a percentage of the photopolymerizablecompound is within a range of 1 to 45% by mass relative to the solidcomponent amount of the liquid solder resist composition; and apercentage of the compound having a cyclic ether skeleton is within arange of 1.5 to 85% by mass relative to the solid component amount ofthe liquid solder resist composition.
 10. The liquid solder resistcomposition according to claim 1, wherein a percentage of thephotopolymerization initiator is within a range of 0.1 to 30% by massrelative to the solid component amount of the liquid solder resistcomposition.